INH and Nix or even Outland definitely didn't deserve as much stuff as they get, and there's a stuffty self-fulfilling prophecy where all the vitriol they receive actively makes them act out more. Maybe not them specifically, but you can't deny the strange cycle of the drama-ee kid getting themselves banned because they acted out after pages upon pages of insults and personal attacks, and then everyone joins in hand to kick them while they're down.
Don't get me wrong, the act that gets them banned isn't justifiable, it's just that it's hard to pin the blame entirely on the impressionable weird kid.
In Sephiroth's case however, I just don't know. Maybe some form of positive feedback loop would have meant the shooting wouldn't have happened, but the guy was deranged. I can't tell you what would have helped him.